When a patient loses a significant amount of blood from a wound or operation site, that blood must be replaced. Due to the risk of blood-transmitted diseases, however, it is desirable to limit the amount of donated blood that is infused. This can be accomplished by collecting the blood lost by the patient, processing the blood with a recovery system to remove any bone chips, blood clots or lipids within the collected blood, and then reinfusing it back into the patient. Salvaging a patient's own blood limits the amount of donated blood the patient must receive, thereby reducing the risk of exposure to disease.
Blood-recovery systems typically suction blood from the wound or operation site through a suction hose leading to a collection reservoir, which is also connected to a vacuum source. The vacuum draws blood into the reservoir via the suction hose. Ordinarily, the path from the hose to the reservoir passes through one or more blood filters. Once the collection reservoir is full, the blood is drained into a collection bag for reinfusion or later use. Generally, in order to drain the blood from the reservoir, it is necessary to break the vacuum within the reservoir by, for example, venting the reservoir to the atmosphere. In many blood-recovery systems, this operation necessarily interrupts the flow of blood since a vacuum is necessary to draw blood into the reservoir.
Various attempts have been made to provide apparatus capable of collecting blood from a patient continuously. U.S. Pat. No. 5,024,613, for example, describes a device that can continuously collect blood from a patient while simultaneously draining the processed blood from the reservoir. The '613 device employs three chambers separated from each other by a series of valves. The middle chamber serves as a transition chamber between a lower-pressure collection chamber and a higher-pressure drainage chamber. This configuration permits isolation of the lower-pressure collection chamber from the higher-pressure drainage chamber, enabling the collection chamber to remain under a constant vacuum even as blood is drained from the drainage chamber. This type of device is complex and requires an extra chamber, thereby increasing its size.
Another apparatus for continuously collecting and reinfusing blood is described in U.S. Pat. No. 4,909,780. That device has a two-chambered reservoir and a rotatable manifold. The manifold can be positioned to allow one chamber to collect blood while the other chamber is reinfusing blood into the patient. This approach is also complex due to the number of parts required.
A simpler apparatus is described in U.S. Pat. No. 5,100,376. With this device, blood is collected under vacuum in a collection chamber that empties into a blood bag. When the weight of the blood collected in the collection chamber exceeds the pressure exerted by the vacuum in the collection chamber, blood drains into the lower bag. A problem with this design is that the vacuum in the collection chamber must be weak enough to allow blood to drain into the blood bag. If the vacuum in the collection chamber exceeds the weight of the blood contained in the collection chamber, no blood will drain into the blood bag.